Flotation is a physico-chemical separation process that utilises the difference in surface properties of the valuable minerals and the unwanted gangue minerals. The theory of froth flotation is complex, involving three phases (solids, water, and froth) with many subprocesses and interactions, and is not completely understood. The subject has been reviewed comprehensively by a number of authors (Sutherland and Wark, 1955; Glembotskii et al., 1972; King, 1982; Leja, 1982; Ives, 1984; Jones and Woodcock, 1984; Schulze, 1984; Fuerstenau et al., 1985; Crozier, 1992; Laskowski and Poling, 1995; Harris et al., 2002; Johnson and Munro, 2002; Rao, 2004), and will only be dealt with briefly here.

The process of material being recovered by flotation from the pulp comprises three mechanisms:

1. Selective attachment to air bubbles (or "true flotation").

2. Entrainment in the water which passes through the froth.

3. Physical entrapment between particles in the froth attached to air bubbles (often referred to as "aggregation").

The attachment of valuable minerals to air bubbles is the most important mechanism and represents the majority of particles that are recovered to the concentrate. Although true flotation is the dominant mechanism for the recovery of valuable mineral, the separation efficiency between the valuable mineral and gangue is also dependent on the degree of entrainment and physical entrapment. Unlike true flotation, which is chemically selective to the mineral surface properties, both gangue and valuable minerals alike can be recovered by entrainment and entrapment. Drainage of these minerals occurs in the froth phase and controlling the...